Patent document 1 describes an example of a vehicle seat reclining device known in the art used for a vehicle seat.
The vehicle seat reclining device of patent document 1 includes two brackets that rotate relative to each other, pawls arranged on a first bracket, and a cam that moves the pawls in a radial direction. Each pawl is biased by the cam to move toward the radially outer side and moves in the radial direction in cooperation with the rotation of the cam. The rotation of the cam moves the pawls toward the radially outer side so that outer teeth of the pawls mesh with inner teeth of a second bracket. This fixes the first bracket to the second bracket. The second bracket includes a pawl restriction portion corresponding to a single predetermined pawl to restrict movement of the predetermined pawl toward the radially outer side. When the rotation angle of the second bracket relative to the first bracket is in a predetermined angle range, the pawl restriction portion engages a limitation portion of the predetermined pawl. This limits movement of each pawl toward the radially outer side and thus allows rotation of the second bracket relative to the first bracket.
However, the technique of patent document 1 has the following problem. Rotation of the second bracket beyond the predetermined angle range biases and pushes the predetermined pawl toward the radially outer side when the limitation portion of the predetermined pawl slides on the pawl restriction portion and reaches an end of the pawl restriction portion. The contact area between the limitation portion of the predetermined pawl and the pawl restriction portion is small at an angle slightly before the predetermined pawl is pushed toward the radially outer side. Thus, when the second bracket rotates to where the predetermined pawl is arranged slightly before the predetermined pawl is pushed toward the radially outer side, an external factor may rotate the cam or a spring may bias and rotate the cam. This will push the predetermined pawl toward the radially outer side, and the pushing force will concentrate at the limitation portion of the predetermined pawl. Thus, the limitation portion of the predetermined pawl or the predetermined pawl may be deformed.
There is also a vehicle seat reclining device in which pawls each include a limitation portion and pawl restriction portions are arranged in correspondence with the limitation portions of the pawls. In this case, when the second bracket rotates beyond the predetermined angle range and the pawls reach an angle where the pawls are pushed toward the radially outer side, the pushing force of the cam produced when an external factor rotates the cam will be dispersed to the pawls. This limits deformation of the pawls. However, in this case, the pawl restriction portions are arranged in correspondence with the pawls. This limits a control angle range of the second bracket to a narrow range in accordance with the number of pawls. The control angle range is an angle range that is the sum of an angle range that restricts movement of the pawls toward the radially outer side and an angle range that allows movement of the pawls toward the radially outer side. Accordingly, in the prior art, it is difficult to limit deformation of the pawls and expand the control angle range.